Generative Power of Normal Forms
Theorem: For every CFG G, there is an   equivalent grammar G’ in
  Chomsky normal form.
Proof: See page 348 in [Meduna: Automata and Languages]
Theorem: For every CFG G, there is an   equivalent grammar G’ in
  Greibach normal form.
Proof: See page 376 in [Meduna: Automata and Languages]
Note: Main properties of CNF and GNF:
CNF: if S Þn w; w Î T* then n = 2|w| – 1
GNF: if S Þn w; w Î T* then n = |w|
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